Functional characterization of a defense-responsive bulnesol/elemol synthase from potato

Terpene synthases (TPSs) produce a variety of terpenoids that play numerous functional roles in primary and secondary metabolism, as well as in ecological interactions. Here, we report the functional characterization of an inducible potatoTPSgene encoding bulnesol/elemol synthase (StBUS/ELS). The expression ofStBUS/ELSin potato leaves was significantly induced in response to both bacterial (Pseudomonas syringae) and fungal (Alternaria solani) infection as well as methyl jasmonate treatment, indicating its role in defense. The leaves exhibited the highestStBUS/ELSexpression followed by the stem with least and similar expression in tuber, sprout and root. Recombinant StBUS/ELS catalyzed the formation of different sesquiterpenes by utilizing farnesyl diphosphate as substrate, and the monoterpene geraniol from geranyl diphosphate. Among the sesquiterpenes formed by StBUS/ELS, elemol was the predominant product followed by alpha-bulnesene, bulnesol and beta-elemene. Further gas chromatography-mass spectrometry (GC-MS) analysis of StBUS/ELS assay products at different injection temperatures revealed elemol and bulnesol as the major products at 275 and 200/150 degrees C, respectively, without much change in the levels of minor products. This indicated thermal rearrangement of bulnesol into elemol at higher temperatures. Transient overexpression ofStBUS/ELSin potato leaves conferred tolerance against the growth of bacteriaP. syringaeandRalstonia solanacearum, and the fungusA. solani. Further, expression analysis of pathogenesis-related (PR) genes inStBUS/ELSoverexpressing leaves showed no significant change in comparison to control, indicating a direct involvement of StBUS/ELS enzymatic products against pathogens. Overall, our study suggested that StBUS/ELS is a pathogen-inducible TPS encoding bulnesol/elemol synthase and could provide a direct role in defense against biotic stress in potato.